Web guide roller, web guide device, and method for guiding web

ABSTRACT

A web guide roller for guiding a web includes a cylindrical crude tube, a nickel plating layer and a chrome plating layer on an outer periphery of the crude tube. Downward depressions and peripheral grooves are formed on the web guide roller. The peripheral grooves are formed along the peripheral direction of the web guide roller. The downward depressions are formed by blast processing onto the nickel plating layer with use of glass beads of an average particle diameter of at least 0.2 mm and at most 1 mm. The average depth D 1  of the downward depressions is between 0.005 mm and 0.05 mm. The depth D 2  of the peripheral grooves is between 0.005 mm and 1 mm. The pitch P between the peripheral grooves is between 0.1 mm and 2 mm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a web guide roller for holding and guiding a flexible belt-like support (hereinafter referred to as a “web”), which is continuously fed, along a predetermined feeding path while holding the web on its cylindrical outer periphery, and relates to a web guide device and a method for guiding the web.

2. Description of the Related Arts

Recently, a demand for a cellulose triacetate film (hereinafter referred to as a “TAC film”), which is used for a protective film of a polarization plate in a liquid crystal display, is increased with expansion of the market for the liquid crystal display. Therefore, many attempts have been made to a solution casting apparatus so as to enhance the productivity of the TAC film.

In the solution casting apparatus, dope solution as a raw material, which is continuously cast on a support such as a casting band or the like, is peeled from the support, and then subjected to a drying process to form the continuous TAC film (hereinafter referred to as a “web”). In order to enhance the productivity of the TAC film, it is necessary for accelerating the feeding speed of the web and reducing the thickness of the web.

However, the acceleration of the web feeding speed leads to the following problem. Many web guide rollers for holding and guiding the web in the feeding direction are provided at a predetermined interval in the solution casting apparatus. When the web is guided by the web guide rollers, air tends to be drawn between the web and the web guide rollers. The amount of the drawn air is increased by accelerating the web feeding speed.

On the other hand, the rigidity of the web is lowered by reducing the web thickness, and wrinkles are easily formed on the web. Therefore, it is necessary to reduce the tension applied to the web being fed. If the tension in feeding the web is reduced, the amount of air drawn between the web and the web guide roller is increased.

When the amount of air, which is drawn between the web and the web guide roller, is increased by accelerating the web feeding speed and reducing the web thickness, the contact between the web and the web guide roller becomes unstable to cause slippage of the web on the web guide roller, so that defects such as scratches and tensile wrinkles occur on the web.

In order to solve the above problem, in the carrying rollers disclosed in Japanese Patent Laid-Open Publications No. 08-175727 and No. 10-77146, the grooves and the projections are formed on the peripheral surface of the carrying roller so as to release the air drawn between the web and the projections into the grooves. Additionally, in the web guide roller disclosed in Japanese Patent Laid-Open Publication No. 2003-146505, the minute objects such as glass beads are sprayed onto the peripheral surface of the roller to form the minute flat or smooth parts and concave portions on the peripheral surface of the roller. The air, which has been drawn in the web, is released into the concave portions, so that it is possible to suppress occurrence of scratches, surface transfer, and wrinkles on the web surface.

However, the carrying rollers disclosed in the Japanese Patent Laid-Open Publications No. 08-175727 and No. 10-77146 are used for carrying a dry film web, e.g. plastic sheet and paper, before it has been coated with the functional material. Therefore, the carrying rollers have a higher web holding force, but when the web immediately after it has been cast or coated with the functional material is fed, the surface transfer on the web may occur.

Meanwhile, the roller disclosed in Japanese Patent Laid-Open Publication No. 2003-146505, there is a problem that the web holding force is changed depending on the web feeding speed. Therefore, the air drawn in the web cannot be released sufficiently into the concave portion when the web feeding speed is accelerated, so that the web is slipped on the web guide roller.

An object of the present invention is to provide a web guide roller, a web feeding device, and a method for guiding the web. This web guide roller is able to hold and guide the web without causing defects such as scratches, tensile wrinkles, surface transfer, and wrinkles on the web, and also maintain the web holding force at a constant level without depending on the web feeding speed even when the web feeding speed is accelerated and when the web thickness is reduced.

SUMMARY OF THE INVENTION

A web guide roller according to the present invention is provided with an approximately cylindrical roller body having an outer periphery, on which a plurality of peripheral grooves and minute depressions are formed. The peripheral grooves are formed along the peripheral direction of the outer periphery of the roller body, and have a depth of at least 0.005 mm and at most 1 mm. The pitch between the peripheral grooves in the axis direction of the roller body is at least 0.1 mm and at most 2 mm. The minute depressions are formed between the adjacent peripheral grooves and connected to each other.

According to a preferable embodiment, a width of the peripheral grooves is at least 0.1 mm and at most 0.5 mm. On the other hand, an average depth of the minute depressions is at least 0.005 mm and at most 0.05 mm. In order to form the minute depressions, minute objects having a size of at least 0.2 mm and at most 1 mm are sprayed onto the outer periphery of the roller body.

The web guide roller is preferably put in a web feeding device which has a supply source for supplying a belt-like web, and holds and feeds the web.

According to the present invention, since the air drawn into the web guide roller upon feeding the web is released through the peripheral grooves and the minute depressions, the web guide roller can surely hold and guide the web without forming the wrinkles on the web due to slippage of the web even when the web feeding speed is accelerated or when the web thickness is reduced. In addition, the defects such as scratches, tensile wrinkles, and surface transfer on the web fed by the web guide roller can be prevented by adjusting the width and depth of the peripheral grooves and the size of the minute depressions.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other subjects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when read in association with the accompanying drawings, which are given by way of illustration only and thus are not limiting the present invention. In the drawings, like reference numerals designate like or corresponding parts throughout the several views, and wherein:

FIG. 1 is a schematic view of a solution casting apparatus;

FIG. 2 is a perspective view of a web guide roller provided in a drying device of the solution casting apparatus;

FIGS. 3A to 3E are partially cross-sectional views showing a process of manufacturing a web guide roller;

FIG. 4 is a partially cross-sectional view of an outer periphery of the web guide roller shown in FIG. 2; and

FIG. 5 is a graph of web holding force versus web feeding speed in the web guide roller of the present invention and in a web guide roller having only downward depressions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiment of the present invention is described in detail. However, the present invention is not limited only to the embodiments to be described therein.

In FIG. 1, in a solution casting apparatus 10, a dope 13 containing polymer 11 and a solvent 12 is continuously cast on a running casting band 14 from a casting die 15 to form a casting film 16 on the casting band 14. The casting film 16 is dried by drying air from a drying duct 17 provided above the casting band 14, and then solvent gas is vaporized from the casting film 16. When the casting film 16 obtains a self-holding property, the casting film 16 is peeled as a wet film 20 from the casting band 14 and fed to a tenter 21. The wet film 20 is dried and stretched in its width direction by the tenter 21 to obtain a film 22. The film 22 out of the tenter 21 is fed to a drying device 23, and dried. Subsequently, the film discharged from the drying device 23 is wound by a winder 24.

The produced film 22 is a cellulose ester film of an average acetylation degree of 58.0% to 62.5%, and has a width of at least 0.3 m and at most 3 m, a thickness of at least 2 μm and at most 200 μm, and surface roughness of 0.5 nm or above.

As shown in FIG. 2, a large number of web guide rollers 31 for guiding a continuous film 30 (hereinafter referred to as “web”), which is continuously fed, is provided in the drying device 23. The web guide roller 31 is constituted of a roller body 32 for holding and guiding the web 30 and shafts 33 fitted to the both ends of the roller body 32. The roller body 32 is formed by applying various kinds of processing (see FIGS. 3A to 3E) to an aluminum cylindrical body 35 (hereinafter referred to as “crude tube”, see FIG. 3) so as to provide a stable web feeding ability. The roller body is not limited to be made of aluminum, but can be made of other material, such as iron, stainless, or carbon fiber reinforced plastic (CFRP).

The following treatment process is applied to the roller body 32. As shown in FIG. 3A, a nickel plating layer 36 having a predetermined thickness is formed on an outer periphery of the crude tube 35. Then, as shown in FIG. 3B, the blast processing is applied onto the surface of the nickel plating layer 36 with use of glass beads (not shown) of an average particle diameter of 0.2 mm to 1 mm. A plurality of upward flanges 40 and downward depressions 41, which have an approximately hemispherical shape, are formed in the nickel plating layer 36 by this blast processing. Most of the downward depressions 41 overlap each other, and each overlapping portion forms an interconnection channel.

In addition to nickel, Fe, Cu, or the like may be used for plating on the tube 35. Additionally, in the blast processing, minute objects such as silica sands and ceramic balls may be used instead of the glass beads. Besides, the downward depressions may have not only the approximately hemispherical shape, but also an approximately polygonal conical shape.

Next, as shown in FIG. 3C, a plurality of peripheral grooves 42 are formed at a predetermined pitch along a peripheral direction of the crude tube 35 by a well-known groove forming method. In this embodiment, although each of the peripheral grooves 42 is triangular groove whose bottom portion is an approximately elliptical cross-section, it may have an approximately semicircular cross-section.

After formation of the peripheral grooves 42, as shown in FIG. 3D, the chrome plating having a predetermined thickness is applied onto the surface of the nickel plating layer 36 having the upward flanges 40, downward depressions 41, and peripheral grooves 42. Thereby, a chrome plating layer 44 is formed on the nickel plating layer 36. Thereafter, as shown in FIG. 3E, the surface of the chrome plating layer 44 is polished to remove some parts in the chrome plating layer 44 corresponding the upward flanges 40, so that smooth parts 46 are formed at positions other than the downward depressions 41 and the peripheral grooves 42. The polishing processing is performed with use of an abrasive cloth or paper, buff, or the like. Instead of the chrome plating, a hard material may be applied, by ceramic spraying or the like, on the surface of the nickel plating layer.

These various processing, shown in FIGS. 3A to 3E, are performed to provide the following conditions. As shown in FIG. 4, an average depth D1 of the downward depressions 41 is at least 0.005 mm and at most 0.5 mm. If the average depth D1 is less than 0.005 mm, only a little amount of air having been drawn when the web is fed is released, and the web holding force is lowered. Meanwhile, if the average depth D1 is over 0.05 mm, it becomes difficult to form the depressions. To make matters worse, the area of the depressions becomes larger as the depth increasing, and as the result the surface transfer is induced on the web being fed.

Meanwhile, a depth D2 of the peripheral grooves 42 is at least 0.005 mm and at most 1 mm, and a pitch P between the peripheral grooves 42 is at least 0.1 mm and at most 2 mm. Since the depth D2 is set to at least 0.005 mm, an adequate amount of air which is drawn when the web is fed is released, and the web 30 is held with an appropriate holding force. Therefore, the defect such as wrinkles does not occur on the web. On the other hand, if the depth D2 is larger than 1 mm, the processing becomes undesirably difficult.

A width D3 of the peripheral grooves 42 is at least 0.1 mm and at most 0.5 mm. Since the width D3 is set to at most 0.5 mm, the defects such as surface transfer and wrinkles on the web 30 do not occur even if the web to be fed is very thin. Meanwhile, if the width D3 is made smaller than 0.1 mm, it becomes difficult to manufacture the web guide roller 31. The holding force to the web 30 can be controlled by adjusting occupation area ratio of the smooth parts 46. In this embodiment, the occupation area ratio of the smooth parts 46 can be at least 0% and less than 100%, preferably 40 to 70% as the practical value.

When fulfilling these conditions, the web guide roller 31 obtains the following advantageous effects in comparison with the prior art rollers. For example, a roller provided with only the downward depressions 41, among the prior art roller, shows web feeding speed dependency, and cannot release enough air, which has been drawn in feeding of the web, when the feeding speed for the web 30 is accelerated. Accordingly, the holding force to the web 30 is lowered. Compared with this, the web guide roller 31 of the present invention can release the air, which cannot be released enough by only the downward depressions 41, through the peripheral grooves 42 even when the feeding speed of the web 30 is accelerated. Therefore, the web holding force of the web guide roller 31 can be maintained constant, regardless of the acceleration of the web feeding speed. Thereby, the web 30 is fed without slipping on the web guide roller 31.

In FIG. 5, a graph 50 shows the web holding force of the web guide roller 31 of the present invention against the feeding speed of the web 30. Meanwhile, a graph 51 shows the web holding force of a roller having only the downward depressions (hereinafter referred to as “a conventional web guide roller”) against the feeding speed of the web 30. Wherein, the web guide roller 31 of the present invention and the conventional web guide roller have the same occupation area ratio of the smooth parts. As shown in the graphs 50 and 51, when the feeding speed of the web 30 is low (e.g. feeding speed S), the web holding forces of the web guide roller 31 and the conventional web guide roller are about the same. As the feeding speed of the web 30 is accelerated, the web holding force of the conventional web guide roller is rapidly lowered, while the web holding force of the web guide roller 31 is maintained at a constant value without being lowered. Accordingly, the speed dependency in the web holding force is not confirmed on the web guide roller 31 of the present invention, and the web 30 can be surely held and guided by the web guide roller 31 even when the web 30 is fed at a high speed.

In the present embodiment, although the web guide roller provided in the drying device of the solution casting apparatus is described, the present invention can also be applied to the web guide roller provided in other apparatuses such as a tenter. The present invention can be applied to the web guide roller provided in not only the solution casting apparatus, but also other producing equipments.

In this embodiment, although the continuous cellulose acylate film is used as the web, a flexible belt-like material or a belt-like object, which uses this flexible belt-like material as a base material and has a worked layer on its surface, may be used. The flexible belt-like material is made from: a plastic film such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, polyamide, or the like; a paper; a paper coated or laminated with α-polyolefins having a carbon number of 2 to 10, such as polyethylene, polypropylene, and ethylene-butene copolymer; and a metallic foil such as aluminum, copper, and tin.

EXPERIMENTAL EXAMPLE

The effect of the web guide roller in the present embodiment is clarified by an experimental example. In this experimental example, the structure of the web guide roller and condition for feeding the web were determined as follows:

1) nickel plating having the thickness of 100 μm was applied onto an outer periphery of a crude tube, which was formed from an aluminum cylindrical body having an outer diameter of 10 cm of specification of the web guider roller. Thereafter, this nickel-plated surface was subjected to blast processing with use of glass beads having an average particle diameter of 800 μm to 900 μm so that the plural downward depressions in an approximately semi-spherical shape were formed. Then, the plural triangular grooves whose bottoms are approximately elliptical cross-sections were formed on the outer periphery of the crude tube along its peripheral direction. Chrome plating having a thickness of 40 μm was applied to the surface having the downward depressions and the grooves to finish the outer periphery. Thereafter, the chrome-plated surface was polished by a buff to form smooth parts at the positions other than the downward depressions and the grooves. With this series of processing, the downward depressions 41, the peripheral grooves 42, and the smooth parts 46 shown in FIG. 4 were formed. The average depth D1 of the downward depressions 41 was set to 0.007 mm (Rz value of the measurement distance of 2.5 mm), the depth D2 and the pitch P of the peripheral grooves 42 were respectively set to at most 0.005 mm and at least 1 mm, and at least 0.1 mm and at most 2 mm. Meanwhile, the occupation area ratio of the smooth parts 46 in the surface area of the roller body 32 was set to 50%.

2) cellulose triacetate having a thickness of 40 μm was used as the web.

3) As to web handling conditions, a web tension was set to 34 kg/m, a web wrap angle was set to 30°, and the web feeding speed was set to at least 20 m/min and at most 400 m/min.

A feeding ability of the web guide roller (the surface quality of the web) prepared as aforementioned was observed and estimated as the web was fed by the web guide roller. Initially, when the depth D2 of the peripheral grooves was less than 0.005 mm, the air drawn when the web was fed cannot be released sufficiently, and the web slipped on the web guide roller. On the other hand, the speed dependency in web holding force of the roller was estimated by comparing the web guide roller of this experimental example with a prior art, downward depression roller. As a result, the web holding force of the downward depression roller was almost lost when the web feeding speed reached at least 100 m/min or more, while the speed dependency of the web holding force was not confirmed in the web guide roller of the present invention, and the web was held sufficiently even at the high-speed feeding.

Although the present invention has been fully described by the way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein. 

1. A web guide roller for holding and feeding a belt-like web, comprising: an approximately cylindrical roller body having an outer periphery; a plurality of peripheral grooves formed on said outer periphery, said peripheral grooves being provided along a peripheral direction of said outer periphery, and having a depth of at least 0.005 mm and at most 1 mm, and being disposed at a pitch of at least 0.1 mm and at most 2 mm in an axis direction of said roller body; and a plurality of minute depressions formed between adjacent said peripheral grooves on said outer periphery, and being connected to each other.
 2. A web guide roller as claimed in claim 1, wherein each of said peripheral grooves has a width of at least 0.1 mm and at most 0.5 mm.
 3. A web guide roller as claimed in claim 1, wherein an average depth of said minute depressions is at least 0.005 mm and at most 0.05 mm.
 4. A web guide roller as claimed in claim 3, wherein minute objects having a size of at least 0.2 mm and at most 1 mm are sprayed onto said outer periphery to form said minute depressions.
 5. A web feeding device for holding and feeding a belt-like web, comprising: a supply source of said web; and a web guide roller comprising: an approximately cylindrical roller body having an outer periphery; a plurality of peripheral grooves formed on said outer periphery, said peripheral grooves being provided along a peripheral direction of said outer periphery, and having a depth of at least 0.005 mm and at most 1 mm, and being disposed at a pitch of at least 0.1 mm and at most 2 mm in an axis direction of said roller body; and a plurality of minute depressions formed between adjacent said peripheral grooves on said outer periphery, and being connected to each other.
 6. A web feeding device as claimed in claim 5, wherein each of said peripheral grooves has a width of at least 0.1 mm and at most 0.5 mm.
 7. A web feeding device as claimed in claim 5, wherein an average depth of said minute depressions is at least 0.005 mm and at most 0.05 mm.
 8. A web feeding device as claimed in claim 7, wherein minute objects having a size of at least 0.2 mm and at most 1 mm are sprayed onto said outer periphery to form said minute depressions.
 9. A web feeding method for holding and feeding a belt-like web in a softened state or a pre-dried belt-like web with a functional material coating, comprising the steps of: supplying said web from a web supply source to a free roller; and holding and guiding said web in a feeding direction by said free roller comprising an approximately cylindrical roller body having an outer periphery, and a plurality of peripheral grooves and minute depressions formed on said outer periphery; wherein said peripheral grooves are provided along a peripheral direction of said outer periphery, and have a depth of at least 0.005 m and at most 1 mm, and are disposed at a pitch of at least 0.1 mm and at most 2 mm in an axis direction of said roller body, and wherein said minute depressions are formed between adjacent said peripheral grooves, and connected to each other. 